If you scroll down to the bottom of the article that Welshwitch linked, there is a link to an article about living donors vs. cadavar donors in children.
And they replace your <i>entire</i> lung on each side with a lobe from each donor, and, according to the website, the living donor needs to be at least 4" taller than the recipient, preferably 6-8(?)" taller, so the donor lobe will fill the chest cavity on each side.